1. Technical Field
The present disclosure relates to the field of digital image processing, and more particularly, the processing applied to digital images of the human eye in identification or authentication applications.
2. Description of the Related Art
Iris recognition is a tested biometric identification technique, provided that the image to which the analysis and identification processing is applied is exploitable. In particular, the performance of the recognition algorithms greatly depends on the sharpness of the image of the iris to be identified. Now, in most applications, and particularly in so-called “embedded” applications (for example, for access control to a mobile telephone or laptop, for an electronic key, etc.), the camera (digital sensor and lens) used has no autofocus device adjusting the focal length according to the distance.
Moreover, to obtain a sufficient resolution of the iris, the images are taken at a relatively short distance, generally in the order of 10 to 30 cm. The result is a small sharpness zone (distance range between the camera and the eye, in which the image is sharp). This small depth of field added to the fact that the eye is spherical can cause differences in sharpness between zones of a same eye image. The user must be very cooperative by standing in a relatively small sharpness zone. Generally, the user moves so as to be positioned at a sharpness distance.
In practice, the images produced by common digital acquisition systems have the following defects:                appearance of white spots resulting from specular reflections of light sources on obstacles existing in the acquisition environment (glasses, sensor optics, etc.),        blurring due to minor eye movements (the pupil and the iris being always visible), and to the optical quality of the sensor,        less sharp contours of image zones (pupil/iris, iris/cornea), due to a lack of focusing, and to the small depth of field of the optical system,        the eyelashes cover a part of the iris.        
When the images are poor, the performance of certain traditional iris identification methods can be diminished, generally as a result of errors in locating the iris.